Determination of phenol, resorcinol and hydroquinone in air samples by synchronous fluorescence using partial least-squares (PLS)

Facile design of FeCu metal-organic frameworks anchored on layer Ti3C2Tx MXene for high-performance electrochemical sensing of resorcinol

This work reports the rational design of a composite material by growing FeCu-MOF-919 on the surface of layered Ti3C2Tx MXene. The introduction of Ti3C2Tx MXene simultaneously weakens the aggregation of FeCu-MOF-919 and Ti3C2Tx MXene, which increases the electrochemical reaction active site of the composite material and improves the electrochemical activity. Interestingly, the FeCu-MOF-919/Ti3C2Tx based sensors were used to detect resorcinol (RS) with a wide linear range (0.5-152.5 μM), excellent sensitivity (0.23 μA μM-1 cm-2), low limit of detection (LOD = 0.08 μM) and outstanding stability. Meanwhile, the sensor shows high repeatability of 1.07 % RSD, reproducibility of 1.47 % RSD and anti-interference performance. What's more, the sensor can be successfully used to detect RS in tap water with good recoveries (96.25-103.37 %, RSD ≤2.18 %), demonstrating that the FeCu-MOF-919/Ti3C2Tx exhibits significant potential as an advanced sensing apparatus for the surveillance of RS in the natural environment.

Effect of Modification of a Laccase-Based Electrochemical Biosensor with Carbon Nanotubes on Signal Separation of Dihydroxybenzene Isomers

This work describes a new electrochemical biosensor for the simultaneous determination of catechol and hydroquinone. A laccase biorecognition layer was deposited using an innovative soft plasma polymerization technique onto a multiwalled carbon nanotube (MWCNT)-modified glassy carbon electrode (GCE) to sufficiently separate catechol (CT) and hydroquinone (HQ) oxidation peaks. The electrochemical analysis carried out for MWCNTs with various morphologies was supported by density functional theory (DFT) calculations showing differences in the electronic structures of both dihydroxybenzene isomers and the MWCNTs forming the biosensor interlayer. The best biosensor peak separation and biosensor analytical parameters were observed for the device containing 75 μg of MWCNTs with a higher internal diameter. For this laccase-based biosensor, a linearity range from 0.1 to 57 μM for catechol and 0.5 to 57 μM for hydroquinone as well as a sensitivity of 0.56 and 0.54 μA/μM for catechol and hydroquinone was observed, respectively. The limit of detection (LOD) values were 0.028 and 0.15 μM for CT and HQ, respectively. This biosensor was also characterized by good selectivity, stability, and reproducibility. It was successfully applied for the quantification of contaminants in the analysis of natural water samples.

Catechol Sensing Performance of Pd-Functionalized Two-Dimensional Polyaramid: A DFT Investigation

Catechol (Cc) molecule adsorption on a pristine and transition metal (TMs = Sc, Pd, and Cu)-functionalized two-dimensional polyaramid (2DPA) monolayer is systematically studied by the first-principles density functional theory method. The weak physisorption (-0.29 eV) and charge transfer of the Cc molecule with p-2DPA result in a very quick recovery time (150 μs), hindering the Cc sensing capability of p-2DPA. Although TM functionalization greatly improved the adsorption ability, the Pd-functionalized 2DPA was shown to be the best choice for Cc adsorption due to the reasonable adsorption energy of -1.39 eV and expedited charge transfer between the Cc and Pd atom. The change of band gap and, hence, the conductivity of the Pd-2DPA system in response to the adsorption of the Cc molecule demonstrate its higher sensitivity than that of p-2DPA. The work function sensitivity of Pd-2DPA upon the Cc adsorption is also investigated. In addition to the change in the electronic properties, the change in the optical properties of Pd-2DPA after Cc adsorption is also analyzed. The structural stability of Pd-2DPA is validated by performing ab initio molecular dynamics simulations at 300 K. The complete desorption of the Cc molecule from Pd-2DPA is attained by annealing the material at 550 K under visible light (τ = 5.4 s) and at 450 K under UV light (τ = 3.7 s). Moreover, the higher diffusion energy barrier of +1.35 eV confirmed that the functionalized Pd atoms did not diffuse through the crystal to form clusters. This study could lay a theoretical foundation for developing possibly new-generation sensors for detecting Cc molecules.

A light-driven photoelectrochemical sensor for highly selective detection of hydroquinone based on type-II heterojunction formed by carbon nanotubes immobilized in 3D honeycomb CdS/SnS2

The ecological environment and public safety are seriously threatened by the typical phenolic contaminant hydroquinone (HQ). Here, using a straightforward physical mixing technique, we created an n-n heterojunction by uniformly immobilizing cadmium sulfide (CdS) nanoparticles on the surface of a three-dimensionally layered, flower-like structure made of tin sulfide (SnS₂). Then, as photosensitizers, carbon nanotubes (CNTs) were added to the CdS/SnS₂ complex to create a type-II heterostructure of CdS/SnS₂/CNTs with synergistic effects. Subsequently, the detector HQ was bound to the modified photoelectrodes, which was accompanied by the hole oxidation of the bound HQ, leading to a significant increase in the photocurrent signal, thus allowing specific and sensitive detection of HQ. Under optimized detection conditions, the proposed photoelectrochemical sensor shows a wide detection range of 0.2 to 100 μM for HQ with a detection limit as low as 0.1 μM. The high accuracy of the sensor was demonstrated by comparison with the detection results of UV-vis spectrophotometry. In addition, the photoelectrochemical sensor exhibits good reproducibility, stability, selectivity, and specificity, providing a light-driven method to detect HQ.

Graphene Oxide-PAMAM Nanocomposite and Ionic Liquid Modified Carbon Paste Electrode: An Efficient Electrochemical Sensor for Simultaneous Determination of Catechol and Resorcinol

In this paper, a simple strategy was proposed for the analysis of catechol by a carbon paste electrode (CPE) modified with graphene oxide-third generation of poly(amidoamine) dendrimer (GO/G3-PAMAM) nanocomposite and ionic liquid (IL). The synthesis of GO-PAMAM nanocomposite was confirmed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), and Fourier transform infrared spectroscopy (FT-IR) techniques. The prepared modified electrode (GO-PAMAM/ILCPE) exhibited good performance to detect catechol with a notable decrease in overpotential and increase in current compared with an unmodified CPE. Under optimum experimental conditions, GO-PAMAM/ILCPE electrochemical sensors indicated a lower limit of detection (LOD) of 0.034 μM and a linear response in the concentration range of 0.1 to 200.0 µM for the quantitative measurement of catechol in aqueous solutions. In addition, GO-PAMAM/ILCPE sensor exhibited an ability to simultaneously determine catechol and resorcinol. It can be found that catechol and resorcinol could be completely separated on the GO-PAMAM/ILCPE with the differential pulse voltammetry (DPV) technique. Finally, a GO-PAMAM/ILCPE sensor was utilized to detect catechol and resorcinol in water samples with recoveries of 96.2% to 103.3% and relative standard deviations (RSDs) of less than 1.7%.

Voltammetric approach for pharmaceutical samples analysis; simultaneous quantitative determination of resorcinol and hydroquinone

A simple and precise analytical approach developed for single and simultaneous determination of resorcinol (RC) and hydroquinone (HQ) in pharmaceutical samples using carbon paste electrode (CPE) modified with 1-Ethyl-3-methylimidazolium tetrafluoroborate as ionic liquid and ZnFe₂O₄ nanoparticle. A significant enhancement in the peak current and sensitivity of the proposed sensor observed by using modifiers in the composition of working electrode compared to bare CPE which is in accordance with the results obtained from electrochemical impedance spectroscopy investigations. Electrochemical investigations revealed a well-defined irreversible oxidation peak for RC over a wide concentration range from 3.0 µM to 500 µM in 0.1 M phosphate buffer solution (pH 6.0) with the linear regression equations of I_p (µA) = 0.0276 C_RC (µM) + 0.5508 (R² = 0.997). The limit of detection and quantification for RC analysis were found to be 1.46 µM and 4.88 µM, respectively. However, the obtained SW voltammograms for simultaneous determination of RC and HQ exhibited a desirable peak separation of about 360 mV potential difference and a satisfactory linear response over the range of 50-700 µM and 5-350 µM with the favorable correlation coefficient of 0.991 and 0.995, respectively. The diffusion coefficient (D) of RC and the electron transfer coefficient (α) at the surface of ZnFe₂O₄/NPs/IL/CPE estimated to be 2.83 × 10^- 4 cm s^- 1 and 0.76. The proposed sensor as a promising and low-cost method successfully applied for determination of RC in commercial pharmaceutical formulations such as the resorcinol cream of 2% O/W emulsion available on the market with the recovery of 98.47 ± 0.04.

Cu-TCPP Nanosheets-Sensitized Electrode for Simultaneous Determination of Hydroquinone and Catechol

It is quite important to develop sensitive, simple, and convenient methods for the simultaneous determination of Hydroquinone (HQ) and Catechol (CC) due to their wide existence, the difficulty of degradation, and the high toxicity. Herein, Cu-TCPP nanosheets were prepared in N,N-dimethylformamide (DMF) through the solvent exfoliation method. The morphology and electrochemical performance of Cu-TCPP were characterized, revealing its stacked sheet structure with abundant pores, a fast electron transfer ability, and a large electrode active area. Using Cu-TCPP nanosheets as the sensitive material to modify the glassy carbon electrodes (Cu-TCPP/GCEs), it was found that they had an obvious enhancement effect on the electrochemical oxidation currents of HQ and CC. The signal enhancement mechanism was explored. The Cu-TCPP nanosheets not only enhanced the accumulation abilities of HQ and CC, but also improved their apparent catalytic rate, displaying high sensitivity for HQ and CC. The values of the detection limit were calculated to be 3.4 and 2.3 nM for HQ and CC. A satisfactory recovery was obtained when this method was used in measuring HQ and CC in the water samples.

Sensitivity Control of Hydroquinone and Catechol at Poly(Brilliant Cresyl Blue)-Modified GCE by Varying Activation Conditions of the GCE: An Experimental and Computational Study

The poly(brilliant cresyl blue) (PBCB)-modified activated glassy carbon electrode (AGCE) shows the catalytic activity toward the oxidation of hydroquinone (HQ) and catechol (CT). The modified electrode can also separate the oxidation peaks of HQ and CT in their mixture, which is not possible with bare GCE. These properties of the modified electrode can be utilized to fabricate an electrochemical sensor for sensitive and simultaneous detection of HQ and CT. In this study, an attempt is made to control the sensitivity of the modified electrodes. This can be accomplished by simply changing the activation condition of the GCE during electropolymerization. GCE can be activated via one-step (applying only oxidation potential) and two-step (applying both oxidation and reduction potential) processes. When we change the activation condition from onestep to twosteps, a clear enhancement inpeak currents of HQ and CT is observed. This helps us to fabricate a highly sensitive electrochemical sensor for the simultaneous detection of HQ and CT. The molecular dynamics (MD) simulation is carried out to explain the experimental data. The MD simulations provide the insight adsorption phenomena to clarify the reasons for higher signals of CT over HQ due to having meta-position –OH group in its structure.

Cobalt Oxide Nanorod-Modified GCE as Sensitive Electrodes for Simultaneous Detection of Hydroquinone and Catechol

An electrochemical sensor based on a cobalt oxide nanorod (Co3O4NR) modified glassy carbon electrode (GCE) (Co3O4NR-GCE) was prepared for simultaneous and selective determination of hydroquinone (HQ) and catechol (CT). Surface morphology and crystallinity of Co3O4NR were investigated employing field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. The structure (16 nm) of the Co3O4 nanorod was observed in the FESEM image. A sharp peak pattern in the XRD survey revealed the following crystal planes in Co3O4NR material: (111), (220), (311), (222), (400), (422), (511), and (440). Electrochemical characterization of modified Co3O4NR-GCE was carried out performing cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Selective and simultaneous detection of HQ and CT was carried out by performing CV and differential pulse voltammetry (DPV) analysis. In both studies, modified Co3O4NR-GCE showed well defined oxidation and reduction peaks for HQ and CT with enhanced peak current, and the oxidation peaks for HQ and CT were observed at 0.152 V and 0.254 V, respectively, in the CV analysis. Scan rate and pH variation analysis were performed to evaluate different kinetic parameters, including charge transfer coefficient (α = 0.56 for HQ and 0.66 for CT), heterogeneous charge transfer rate constant (ks = 56 for HQ and 72 for CT), and the number of electrons involved in HQ and CT oxidation. Quantitative analysis of HQ and CT was studied by observing the current response of DPV analysis with respect to concentration variation. Here, the detection limit was calculated as 0.2 µM for HQ with a linear concentration range of 5–200 µM, and 0.4 µM for CT with a linear concentration range of 5–150 µM. The practical applicability of the proposed sensor was investigated using sample solutions prepared in tap water. The reported sensor showed impressive selectivity towards HQ and CT in the presence of common interferents.

An experimental and theoretical approach to electrochemical sensing of environmentally hazardous dihydroxy benzene isomers at polysorbate modified carbon paste electrode

It is well known that, surfactants provide a neutral, positive and/or negative charge on the electrode surface by forming a monolayer, which in turn affects the charge transfer and redox potential during the electroanalysis process. However, the molecular level understanding of these surfactant-modified electrodes is worth investigating because the interaction of the analyte with the electrode surface is still unclear. In this report, we used quantum chemical models based on computational density functional theory (DFT) to investigate the polysorbate 80 structure as well as the locations of energy levels and electron transfer sites. Later, the bare carbon paste electrode (bare/CPE) was modified with polysorbate 80 and used to resolve the overlapped oxidation signals of dihydroxy benzene isomers. The m/n values obtained at polysorbate/CPE was approximately equal to 1, signifying the transfer of same number of protons and electrons. Moreover, the analytical applicability of the modified electrode for the determination of catechol (CC) and hydroquinone (HQ) in tap water samples gave an acceptable recovery result. Overall, the application of DFT to understand the molecular level interaction of modifiers for sensing applications laid a new foundation for fabricating electrochemical sensors.

Novel delipidated chicken feather waste-derived carbon-based molybdenum oxide nanocomposite as efficient electrocatalyst for rapid detection of hydroquinone and catechol in environmental waters

Chicken poultry industry produces a vast amount of feather waste and is often disposed into landfills, creating environmental pollution. Therefore, we explored the valorization of chicken feather waste into lipids and keratinous sludge biomass. This study demonstrates the successful utilization of keratinous sludge biomass as a unique precursor for the facile preparation of novel keratinous sludge biomass-derived carbon-based molybdenum oxide (KSC@MoO₃) nanocomposite material using two-step (hydrothermal and co-pyrolysis) processes. The surface morphology and electrochemical properties of as-prepared nanocomposite material were analyzed using HR-SEM, XRD, XPS, and cyclic voltammetric techniques. KSC@MoO₃ nanocomposite exhibited prominent electrocatalytic behavior to simultaneously determine hydroquinone (HQ) and catechol (CC) in environmental waters. The as-prepared electrochemical sensor showed excellent performance towards the detection of HQ and CC with broad concentration ranges between 0.5-176.5 μM (HQ and CC), and the detection limits achieved were 0.063 μM (HQ) and 0.059 μM (CC). Furthermore, the developed modified electrode has exhibited excellent stability and reproducibility and was also applied to analyze HQ and CC in environmental water samples. Results revealed that chicken feather waste valorization could result in sustainable biomass conversion into a high-value nanomaterial to develop a cost-effective electrochemical environmental monitoring sensor and lipids for biofuel.

A highly sensitive electrochemical biosensor for the detection of hydroquinone based on magnetic covalent organic frameworks and enzyme for signal amplification

Possessing prominent customization in structural design as well as unique physicochemical properties, covalent organic frameworks (COFs) show great potential in biosensing field. In this paper, we prepared a novel COF...

Picomolar level electrochemical detection of hydroquinone, catechol and resorcinol simultaneously using a MoS2 nano-flower decorated graphene

A Graphene-Molybdenum disulphide nanocomposite was developed for the simultaneous electrochemical detection of dihydroxy benzene isomers attributed to the structural aspects.

Barium titanate nanoparticle-based disposable sensor for nanomolar level detection of the haematotoxic pollutant quinol in aquatic systems

Barium titanate nanoparticles synthesized by a simple co-precipitation method and applied for the electrochemical detection of quinol.

Photocatalytic performance, anti-bacterial activities and 3-chlorophenol sensor fabrication using MnAl2O4·ZnAl2O4 nanomaterials

A MnAl₂O₄·ZnAl₂O₄ nanomaterial was synthesized by co-precipitation and characterized by XRD, SEM, EDS, TEM, AFM, FTIR, PL, CV and EIS. The photocatalytic activity of the nanocomposite against MV dye and its MDR anti-bacterial functions were studied. The nanocomposite shows excellent photocatalytic as well as anti-bacterial activity. A MnAl₂O₄·ZnAl₂O₄ nanomaterial/Nafion/GCE electrode was fabricated and implemented as the working electrode of a 3-CP sensor. The sensor exhibited good sensitivity, with the lowest detection limit, fast response time, large linear dynamic range (LDR), and long-term stability in the chemical environment. The estimated sensitivity is 70.07 μA mM^-1 cm^-2. The LDR, limit of detection (LOD), and limit of quantification (LOQ) are 0.1 nM to 0.01 M, 0.0014 ± 0.0001 nM, and 0.004 nM, respectively. The MnAl₂O₄·ZnAl₂O₄ nanomaterial/Nafion/GCE is a promising fabricated sensor probe for the selective detection of 3-CP for the environmental safety and healthcare fields on a large scale.

Eco-friendly fluorimetric approaches for the simultaneous estimation of the co-administered ternary mixture: etoposide, moxifloxacin and nalbuphine

Antineoplastic drugs, etoposide (ETO), are widely used in leukaemia. A patient with leukaemia has a relative infection with pneumonia treated by fluoroquinolones as moxifloxacin HCL (MOX). Because opioid analgesic as nalbuphine HCL (NAL) does not have a ceiling dose, it is used to manage the distasteful sensory in leukaemia. Consequently, green methods for synchronous spectrofluorimetric quantification of a ternary mixture of ETO, MOX and NAL were developed. The first approach relies simply on the estimation of MOX at 371 nm by conventional synchronous fluorimetric technique (Δλ of 60 nm). The second approach depends on applying the first derivative synchronous fluorimetric technique (Δλ of 60 nm) for simultaneous estimation of ETO and NAL at 257 and 273 nm, respectively. A good linear correlation was obtained in the ranges of 0.04-0.40, 0.10-1.00 and 0.50-5.00 µg ml-1 for MOX, ETO and NAL, respectively. Moreover, the proposed approaches were successfully applied for the estimation of the studied drugs in the pharmaceutical dosage forms. Additionally, the synchronous assessment of ETO, MOX and NAL in the spiked human urine was successfully attained by the facile protein precipitation technique. The mean % recoveries in spiked human urine were 99.49, 98.07 and 98.48 for MOX, ETO and NAL, respectively.

An efficient electrochemical sensing of hazardous catechol and hydroquinone at direct green 6 decorated carbon paste electrode

In this proposed work, direct green 6 (DG6) decorated carbon paste electrode (CPE) was fabricated for the efficient simultaneous and individual sensing of catechol (CA) and hydroquinone (HY). Electrochemical deeds of the CA and HY were carried out by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at poly-DG6-modfied carbon paste electrode (Po-DG6-MCPE). Using scanning electron microscopy (SEM) studied the surface property of unmodified CPE (UCPE) and Po-DG6-MCPE. The decorated sensor displayed admirable electrocatalytic performance with fine stability, reproducibility, selectivity, low limit of detection (LLOD) for HY (0.11 μM) and CC (0.09 μM) and sensor process was originated to be adsorption-controlled phenomena. The Po-DG6-MCPE sensor exhibits well separated two peaks for HY and CA in CV and DPV analysis with potential difference of 0.098 V. Subsequently, the sensor was practically applied for the analysis in tap water and it consistent in-between for CA 93.25–100.16% and for HY 97.25–99.87% respectively.

Tuning Electrocatalytic Aptitude by Incorporating α-MnO2 Nanorods in Cu-MOF/rGO/CuO Hybrids: Electrochemical Sensing of Resorcinol for Practical Applications

In this study, Cu-MOF/rGO/CuO/α-MnO₂ nanocomposites have been fabricated by a one-step hydrothermal method and used in the voltammetric detection of resorcinol (RS). The poor conductivity of MOFs in the field of electrochemical sensing is still a major challenge. A series of Cu-MOF/rGO/CuO/α-MnO₂ nanocomposites have been synthesized with varying fractions of rGO and with a fixed amount of α-MnO₂ via a facile method. These nanocomposites are well characterized using some sophisticated characterization techniques. The as-prepared nanohybrids have strongly promoted the redox reactions at the electrode surface due to their synergistic effects of improved conductivity, high electrocatalytic activity, an enlarged specific surface area, and a plethora of nanoscale level interfacial collaborations. The electrode modified with Cu-MOF/rGO/CuO/α-MnO₂ has revealed superior electrochemical properties demonstrating linear differential pulse voltammetry (DPV) responses from a 0.2 to 22 μM RS concentration range (R² = 0.999). The overall results of this sensing podium have shown excellent stability, good recovery, and a low detection limit of 0.2 μM. With excellent sensing performance achieved, the practicability of the sensor has been evaluated to detect RS in commercial hair color samples as well as in tap water and river water samples. Therefore, we envision that our hybrid nanostructures synthesized by the structural integration strategy will open new horizons in material synthesis and biosensing platforms.

High-performance electrochemical sensing platform based on sodium alginate-derived 3D hierarchically porous carbon for simultaneous determination of dihydroxybenzene isomers

Three-dimensional hierarchically porous carbon (denoted as SA-900) with a microporous, mesoporous and macroporous structure was facilely fabricated via direct carbonization of sodium alginate. SA-900 was fully characterized by N₂ adsorption-desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction and Raman spectroscopy to confirm its structure. SA-900 was coated onto a glassy carbon electrode surface to construct an ultrasensitive electrochemical sensing platform (SA-900/GCE). Electrochemical behaviors of hydroquinone (HQ), catechol (CC) and resorcinol (RC) on the SA-900/GCE surface were investigated, and it was found that SA-900 possesses excellent electrocatalytic activity towards them. Experimental conditions including carbonization temperature, pH value, SA-900 concentration, accumulation potential and accumulation time were optimized for quantitative assay. Under optimized conditions, linear ranges for simultaneous determination of HQ, CC and RC are 0.05-1.50 μM, 0.05-1.50 μM and 0.50-15.00 μM, respectively. Detection limits for HQ, CC and RC are calculated to be 0.0183 μM, 0.0303 μM and 0.3193 μM (S/N = 3). The SA-900/GCE based electrochemical sensing platform is applied for determining HQ, CC and RC in lake water samples with satisfactory results.

Fabrication of an Extremely Cheap Poly(3,4-ethylenedioxythiophene) Modified Pencil Lead Electrode for Effective Hydroquinone Sensing

Hydroquinone (HQ) is one of the major deleterious metabolites of benzene in the human body, which has been implicated to cause various human diseases. In order to fabricate a feasible sensor for the accurate detection of HQ, we attempted to electrochemically modify a piece of common 2B pencil lead (PL) with the conductive poly(3,4-ethylenedioxythiophene) or PEDOT film to construct a PEDOT/PL electrode. We then examined the performance of PEDOT/PL in the detection of hydroquinone with different voltammetry methods. Our results have demonstrated that PEDOT film was able to dramatically enhance the electrochemical response of pencil lead electrode to hydroquinone and exhibited a good linear correlation between anodic peak current and the concentration of hydroquinone by either cyclic voltammetry or linear sweep voltammetry. The influences of PEDOT film thickness, sample pH, voltammetry scan rate, and possible chemical interferences on the measurement of hydroquinone have been discussed. The PEDOT film was further characterized by SEM with EDS and FTIR spectrum, as well as for stability with multiple measurements. Our results have demonstrated that the PEDOT modified PL electrode could be an attractive option to easily fabricate an economical sensor and provide an accurate and stable approach to monitoring various chemicals and biomolecules.

Fluorescence "turn-on" of silicon-containing nanoparticles for the determination of resorcinol

A fluorescent nanosensor based on silicon-containing nanoparticles (Si CNPs) with green fluorescence (FL) was prepared by one-step method. The prepared Si CNPs emitted green FL at 470 nm under the excitation at 350 nm. The FL signal of Si CNPs reveals an obvious enhancement in the presence of resorcinol (RC), due to the passivation of surface trap states of Si CNPs via the binding of OH group of RC with the NH group of Si CNPs, which allowed the formation of new radiative electron-hole recombination centers. This was confirmed by some analytical experiments performed on zeta potential, FL lifetime steady state, and the FTIR spectra. Most importantly, this nanosensor could selectively determine RC with high sensitivity and without interference from hydroquinone (HQ) and catechol (CT) as RC isomers. RC was detected in the linear range 0.05-40 μM, with a detection limit of 0.012 μM. The synthesized nanosensor was applied to the determination of RC in fresh fruit juice and water samples. The collected results confirmed the feasibility of our approach with high accuracy.

A three-electrode integrated electrochemical platform based on nanoporous gold for the simultaneous determination of hydroquinone and catechol with high selectivity

A novel integrated electrochemical platform was built for the simultaneous determination of hydroquinone and catechol.

Ultrasensitive voltammetric detection of benzenediol isomers using reduced graphene oxide-azo dye decorated with gold nanoparticles

The detection of phenolic compounds, i.e. resorcinol (RC) catechol (CC) and hydroquinone (HQ) are important due to their extremely hazardous impact and poor environmental degradation. In this work, a novel and sensitive composite of electrochemically reduced graphene oxide-poly(Procion Red MX-5B)/gold nanoparticles modified glassy carbon electrode (GCE/ERGO-poly(PR)/AuNPs) was assembled for voltammetric detection of benzenediol isomers (RC, CC, and HQ). The nanocomposite displayed high peak currents towards the oxidation of RC, HQ, and CC compared to non-modified GCE. The peak-to-peak separations were 0.44 and 0.10 V for RC-CC and CC-HQ, respectively. The limit of detections were 53, 53, and 79 nM for HQ, CC, and RC with sensitivities of 4.61, 4.38, and 0.56 μA/μM (S/N = 3), respectively. The nanocomposite displayed adequate reproducibility, besides good stability and acceptable recoveries for wastewater and cosmetic samples analyses.

Fabrication of Efficient and Selective Modified Graphene Paste Sensor for the Determination of Catechol and Hydroquinone

An electrochemical sensor, based on a graphene paste electrode (GPE), was modified with a polymerization method, and the electrochemical behavior of catechol (CC) and hydroquinone (HQ) was investigated using electroanalytical methods like cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The effect of CC at the modified electrode was evidenced by the positive shift of the oxidation peak potential of CC at the poly (rosaniline)-modified graphene paste electrode (PRAMGPE) and the nine-fold enhancement of the peak current, as compared to a bare graphene paste electrode (BGPE). The sensitivity of CC investigated by DPV was more sensitive than CV for the analysis of CC. The DPV method showed the two linear ranges of 2.0 × 10−6–1.0 × 10−5 M and 1.5 × 10−5–5 × 10−5 M. The detection limit and limit of quantification were determined to be 8.2 × 10−7 and 27.6 × 10−7 M, respectively. The obtained results were compared successfully with respect to those obtained using the official method. Moreover, this sensor is applied for the selective determination of CC in the presence of HQ. The high sensitivity, good reproducibility, and wide linear range make the modified electrode suitable for the determination of CC in real samples. The practical application of the sensor was demonstrated by determining the concentration of CC in water samples with acceptable recoveries (97.5–98%).

Individual and Simultaneous Voltammetric Determination of Ultra-Trace Environmental Contaminant Dihydroxybenzene Isomers Based on a Composite Electrode Sandwich-like Structure

An advanced electroanalytical technique for the simultaneous assessment of environmental contaminant dihydroxybenzene isomers, catechol (CC), hydroquinone (HQ), and resorcinol (RC), has been investigated using palladium nanoparticles (PdNPs) incorporated onto a poly(1,5-diaminonaphthalene) (DAN) matrix over a glassy carbon electrode (GCE). Concurrently, these types of phenols can be assessed by the PdDAN/GCE modified electrode employing square wave voltammetry and cyclic voltammetry (CV) techniques under optimal conditions. This modified electrode has demonstrated linear responses for CC, HQ, and RC from 50.0 to 1000.0 mM; concomitantly, low detection limits of 0.22, 0.22, and 0.47 nM and low quantification limits of 0.740, 0.758, and 1.590 nM, have been, respectively, shown. Successfully, the simultaneous assessment of the three isomers in river stream water, tap water, and underground water has been implemented via the modified electrode under investigation. In comparison to reported studies, the PdDAN catalytic electrode has shown an effective sensitivity, leverage reproducibility, long-term stability, and excellent anti-interference capability for the determination of dihydroxybenzene isomers.

Poly (Adenine) Modified Graphene-Based Voltammetric Sensor for the Electrochemical Determination of Catechol, Hydroquinone and Resorcinol

Objective:

This paper presents the application of Poly (Adenine) Modified Graphene Paste Electrode (PAMGPE) for the analysis of Catechol (CC) with Resorcinol (RC) and Hydroquinone (HQ) by a voltammetric technique.

Methods:

Electropolymerization technique was utilized for the modification of the sensor surface. The electrode surface was characterized by Field Emission Scanning Electron Microscopy (FE-SEM). Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) were used to study the redox behavior of CC, RC and HQ.

Results:

Oxidation peak current of CC increased linearly with the concentration of CC in the range from 2×10-6- 8×10-6 M and 1×10-5-1.5 ×10-4 M with a detection limit of 2.4×10-7 M. The practical application of the developed sensor was verified as exact for the determination of CC in water sample.

Conclusion:

The stability, repeatability, and reproducibility of the developed electrode were studied and established good characteristics. Furthermore, the PAMGPE was examined for the simultaneous determination of CC, RC and HQ.

Synchronous fluorescence spectroscopy combined with chemometrics for determination of total phenolic content and antioxidant activity in different tea types

BACKGROUND

The aim of this study is to monitor the antioxidant activity (AA) and total phenolic content (TPC) variations of different kinds of teas depending on the infusion temperature and time by using synchronous fluorescence spectroscopy (SFS) combined chemometrics as a rapid method. In this study, black tea, oolong tea, green tea, and green tea powder (matcha) samples were brewed at 80 °C and 96 °C for 2.5 to 30 min. Synchronous fluorescence spectra were recorded at different wavelength interval (Δλ) values for optimal models. AA and TPC of tea samples were determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay and Folin-Ciocalteu methods as reference methods, respectively. Partial least square (PLS) method was used for correlation between reference methods and SFS method.

RESULTS

Results showed that SFS combined with chemometrics could be an alternative rapid way to monitor TPC and AA of teas with 0.932 and 0.918 of validation R² values in fermented teas (black tea-oolong) while with 0.961 and 0.860 of validation R² values in non-fermented teas (green tea and green tea powder), respectively. Limit of detection (LOD) and root mean square error of prediction (RMSEP) values were ≤ 6.61 μg mL^-1 and ≤ 17.42, respectively.

CONCLUSION

Based on the lowest R² value (0.860) on TPC analysis, the proposed method is more appropriate for AA analysis of green tea and green tea powder. Furthermore, infusion time was more effective for obtaining different amounts of TPC and AA in fermented tea types while only infusion temperature was effective on green tea and green tea powder samples. Therefore, obtained calibration-validation models gave better results for fermented tea types.

Quantification of microbiota-related phenols and aromatic acids in mouse feces of a diabetic nephropathy model by simultaneous BDAPE derivatization using ultra-performance liquid chromatography-tandem mass spectrometry

In the intestine, several phenols and aromatic acids are generated by microbiota and are highly related to the formation of uremic toxins. Herein, we developed a new derivatization reagent, 2-bromo-1-[4-(dimethylamino)phenyl] ethyl ketone (BDAPE), that reacted simultaneously with phenols and aromatic acids. Following a reaction within 2 h at 60 °C in the presence of 200 mM potassium carbonate (K₂CO₃), the obtained BDAPE derivatives were separated on a reversed-phase C18 column and quantified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) in positive electrospray ionization mode. This method allowed a lower limit of quantification (LLOQ) of 0.090 μΜ for 3-indolepropionic acid (3IPA), indole-3-acetic acid (3IAA), p-cresol (PC), benzoic acid (BA), and phenol (PN); 0.30 μΜ for phenylacetic acid (PAA); 0.45 μΜ for 4-hydroxyphenylacetic acid (4HPAA); and 0.60 μΜ for 3-phenylpropionic acid (PPA). Methodological validation further demonstrated acceptable accuracy (%RE < 16.1) and precision (%RSD < 16.2), suggesting that this is a sensitive and robust method for simultaneous quantification of phenols and aromatic acids. The method was successfully applied to analyze these microbiota-related analytes in mouse feces of a diabetic nephropathy model. Graphical abstract.